Freshwater Fishes

Aquatic Ecology

Fishes Diversity

• Most species-rich group of vertebrates, >24,000

• All other vertebrates approximately 23,500 (Table 5.1, p.124)

• 3 Classes:– Agnatha– Chondrichthyes– Osteichthyes

• Bony Fishes = Teleosts

Why are there so many FW fish species?

productivity: freshwater habitats are generally more productive than marine environments– shallower more sunlight ⇒ ⇒

more photosynthesis– more terrestrial input of

nutrients• isolation: FW habitats tend to

be isolated by:– drainages, drought, landslides,– waterfalls, plate tectonics, etc.

⇒ impedes gene flow ⇒ can lead to explosive speciation when new habitats are invaded

• in contrast, marine habitats are more connected, separated mainly by continents)

Cause of high rate of speciation in FW: rapid evolution

Evolution: a change in gene frequencies between generations Causes of evolution:

1. Natural selection: best adapted individuals pass on more genes to the next generation than do less adapted individuals

2. Genetic drift: random processes cause certain genes to disappear from or become fixed in a population

3. Gene flow: genes enter a population from outside sources4. Sexual selection: selected genes become more common in the

next generation when one or both sexes (1) prefer to mate with individuals with certain phenotypes that (2) have a genetic basisBUT…

• speciation will only occur if evolving populations become reproductively isolated

Causes of reproductive isolation

1. Physical (geographic) isolation: populations cannot come into contact due to physical barriers

2. Environmental isolation: populations live in different habitats

3. Behavioral isolation: mating behaviors of individuals from different populations are too different for successful reproduction

4. Mechanical isolation: sex organs are too different formating to occur

5. Physiological isolation: hybrid offspring are not formed or have lower fitness than pure offspring

Types of Fishes in Freshwater• Primary FW fishes: families strictly confined to FW, cannot tolerate

SW; have a long evolutionary history in FW- e.g., characins, minnows, catfishes, sunfishes

• Secondary FW fishes: families generally restricted to FW but may occasionally tolerate SW; originally of marine origin

- e.g., cichlids, poecilids• Freshwater representatives of marine families (“peripheral”)

- e.g., sculpins, puffers, gobies, stingrays• • Diadromous fishes (“peripheral”): migrate from SW to FW or

vice versa at different stages in their life cycles- e.g. salmon, smelt, eels

• Euryhaline marine visitors– e.g., sharks, snappers

Orders to Research

1. Clupeiformes – Herring (shad)

2. Cypriniformes – Minnows (carp, dace, koi)

3. Esociformes – Pike (pickerel, mudminnows)

4. Perciformes – Perch (bass, darters, walleye, sunfish, drums)

5. Salmoniformes – Salmon (trout, whitefish)

6. Siluriformes – Catfish

7. Cyprinodontiformes – Mosquitofish (guppies)

Ecology of Fishes: Habitat & Distribution

• Physical factors affecting distributions:

• temperature

• light (turbidity)

• gradient (steepness)

• substrate

• flow regime

• size of water body

Chemical factors:

• pH

• dissolved oxygen

• salinity

• dissolved ions

• anthropogenic pollutants

Biological factors:

• predator-prey interactions

• competitive interactions

• symbiotic interactions

Freshwater Habitats:

• streams

• rivers

• puddles

• ponds

• lakes

• hot (& cold) springs

• caves

Physical and chemical factors:Zonation of Temperate Streams

• Zones

• erosional

• intermediate

• depositional

• Fishes tend to occur in areas with particular physical and chemical characteristics

1. Erosional zone• physical characteristics:

high gradient, rocky bottom, swift current, cold water; long riffles and small pools are main habitat

• typical fishes: streamlined, active swimmers (i.e.,trout), small bottom-dwellers (sculpins and dace)

2. Intermediate zone

• physical characteristics: moderate gradients, warm water, intermediate current; main habitats are shallow riffles and deep pools with rocky bottoms or mud bottoms, and runs with undercut banks

• typical fishes: minnows, suckers, sunfishes, darters, catfishes

3. Depositional zones

• physical characteristics: lower reaches of rivers, where waters are warm, turbid, and slow flowing and stream bottom is generally muddy; aquatic plants can be common

• typical fishes: deep-bodied forms that are bottom feeders (carp, suckers), planktivores (shads), invertivores (sunfish), or predators (centrarchid basses). (Same as those found in nearby lakes)